I usually dive a sea life - either the micro 2.0 or the DC2000, depending on what I'm doing and how much gear I want to haul around underwater - but I occasionally go for the big DSLR setup too (if it is worth the risk of flooding. I always remind myself that flooding will happen - it isn't an 'if', it's a 'when').
How much photo experience does your daughter have? If she's really comfortable underwater and very used to a DSLR she'll pick up the DC2000 quickly and not be too frustrated by it but may find the micro tedious and limiting (unless she's totally fine with using a point and shoot). If she's less experienced with photo equipment or not super comfortable with diving yet, the micro will be really easy for her to get used to using while diving. If she's really comfortable diving, the DC2000 will be simple for her to pick up the basics while allowing her to move into the more technical aspects without being overwhelmed early on.
Like others have said, the lag is only really an issue on the DC2000 if you are shooting in raw - what type of photography does she want to do? The lag and auto focus isn't an issue for tiny macro stuff where speed isn't necessarily needed and she has time to compose the shot. For other things, auto settings minimize the lag quite a bit.